Was looking through a translation of MS Era, and I noticed something interesting in a couple of the pictures. In addition to the Zaku II and Dom variants portrayed, there's also a portrayal of a Gouf variant among them: here and here.

besides, taking them all to be new mecha designs and not just Izubuchi's way of drawing old mecha designs introduces mind-bending paradoxes, like Zaku II Kais apparently in service in the Zeon forces before the One Year War, and down that road lies only madness.

when the book was published they had the team who did 0080 do the artwork and they used Izubuchi's line art regardless of the time period the image is said to take place. This book led to the theory that the 0080 ms were originally meant to be imagined 0079 ms and not late war models based on zeta era ms.

If i re-member right MS Era was an anniversary art book with the story that these were news photos taken during the Early UC era including an image of the back of the RX-78-2 Izubuchi did to go with the NT-1 line art. The book is one artists interpretation of events that took place between UC 0001 to 0080 if anything some of these units may also be reverse homages of Zeta, ZZ, and CCA MS. The book was notable for giving us artwork of the MS-01. the hand held zaku sheld seems to be inspired by both the gouf shield and the Hi-zack shield though.